Typically, a low air pressure switch is adapted for a pneumatic line of large-sized vehicles such as busses, trucks, etc. The low air pressure switch installed in a pneumatic line, for example, a line of a pneumatic brake system, functions to detect a drop in air pressure below a predetermined level. The low air pressure switch is designed to turn on when the air pressure drops below a certain level. An alarming light is turned on in response to the turn-on state of the switch, thereby, generating a sound so that a driver is immediately informed of the drop in air pressure.
A conventional low air pressure switch includes a switch body and a switch cover combined, thus forming a body of the low air pressure switch. The body includes a diaphragm operating in response to air pressure supplied through an air inlet and outlet. A plunger is elastically supported by a spring in cooperation with the diaphragm. A contact plate is provided in a direction opposite to the direction to which the plunger is moved, thus forming a selective on and off contact with respect to the plunger. The air inlet and outlet is engaged to an airline of an automobile and a passage through which air is introduced and released. The diaphragm turns a switch contact point on and off based on a pressure state of air introduced through the air inlet and outlet. A screw assembly is engaged to an air vent block which is engaged to a rear side of the switch cover and is connected by a wire of a connector through a wiring connection member. The connector is connected with a wire harness of the automobile based on a lead wire type.
Therefore, power supplied to the plunger is supplied through the wire of the connector, the wiring connection member, the screw assembly, the air vent block, and the spring. The contact plate is connected with an automobile body through a contact cup and a switch body, thus forming a conduction circuit. In addition, a water resistance rubber cap is engaged from an external side of the switch cover, thus protecting the interior of the switch and the wiring connection portion, thus, in theory, preventing corrosion when moisture is introduced.
In the above-described conventional low air pressure switch, even though the lead wire connection part is protected from moisture by means of a rubber cap, the rubber cap may be corroded and deformed over time and moisture may permeate through a discharge passage of air in the spring chamber along the wire. Thereby, the interior of the switch often becomes corroded, thus losing inherent functions of the switch.
Because the low air pressure switch mainly functions to check air pressure of pneumatic brake systems, the malfunction of the switch can cause a critical problem in safety. Therefore, a certain resolution with respect to the above problem is urgently needed in the industry.